Polyurethane prepolymers having alkoxysilane end groups, method for the production thereof and their use for the production of sealants

ABSTRACT

This invention relates to polyurethane prepolymers which comprise alkoxysilane terminal groups and which are based on special, very high molecular weight polyurethane prepolymers, to a method of producing them and to their use as binders for low-modulus sealing materials.

This invention relates to polyurethane prepolymers which comprisealkoxysilane terminal groups and which are based on special, very highmolecular weight polyurethane prepolymers, to a method of producing themand to their use as binders for low-modulus sealing materials.

Alkoxysilane-functional polyurethanes which crosslink via a silanecondensation polymerisation reaction have long been known. A reviewarticle on this topic is to be found. for example. in “Adhesives Age”4/1995, pages 30 et seq. (authors: Ta-Min Feng, B. A. Waldmann).Alkoxysilane-terminated, moisture-curing, single-component polyurethaneof this type are increasingly being used as flexible coating, sealingand adhesive compositions in the building industry and in the automobileindustry. In applications such as these, considerable demands are madeon the extensibility and adhesion capacity and on the curing rate. Inparticular, the level of properties required in the building sectorcannot be achieved in its entirety by prior art systems.

EP-A-596 360 describes alkoxysilyl-functional polyurethane prepolymerswhich are suitable as binders for sealing materials. However, theproducts which are explicitly described in this patent application arenot suitable for the production of flexible, low-modulus sealingmaterials such as those used in the building sector.

The property profile for sealing materials in the building sector isspecified in detail in DIN ISO 11600. The same observation is alsoapplicable as regards the most recently published subsequent patentapplications to EP-A 596 360, namely EP-A 831108 and EP-A 807 649. Theproducts described in these prior art patents are suitable for theproduction of high-modulus sealing materials such as those which areused the engineering field, but are not suitable for the production oflow-modulus sealing materials for building.

The object of the present invention was therefore to providepolyurethane prepolymers which comprise alkoxysilane terminal groups andwhich are suitable as binders for the production of low-modulus sealingmaterials. It has proved possible to achieve this object by theprovision of polyurethane prepolymers which comprise alkoxysilaneterminal groups and which are described in detail below: these are basedon special, very high molecular weight polyurethane prepolymers.

The present invention relates to polyurethane prepolymers which comprisealkoxysilane terminal groups and which are produced by the reaction of

A) linear polyurethane prepolymers, produced by the reaction of

i) an aromatic, aliphatic or cycloaliphatic diisocyanate componenthaving an NCO content of 20% to 60%. with

ii) a polyol component which comprises a polyoxyalkylene diol as itsmain component and which has a molecular weight of 3000 to 20,000, with

B) compounds of formula (I) which comprise alkoxysilane and amino groups

 wherein

R and R′ represent identical or different alkyl radicals comprising 1 to8 carbon atoms, preferably 1 to 4 carbon atoms, and

X, Y, Z represent identical or different C₁-C₈ alkyl or C₁-C₈ alkoxyradicals comprising 1 to 4 carbon atoms, with the proviso that at leastone of the radicals represents a C₁-C₈ alkoxy group,

characterised in that polyurethane prepolymers A) have an averagemolecular weight from 15,000 to 50,000, preferably from 20,000 to40,000, as calculated from their NCO content and NCO functionality.

X, Y and Z in formula (I), independently of each other, preferablyrepresent methoxy or ethoxy.

The present invention also relates to a method of producing polyurethaneprepolymers comprising alkoxysilane terminal groups by the reaction of

A) linear polyurethane prepolymers with an average molecular weight from15,000 to 50,000 as calculated from their NCO content and NCOfunctionality, with

B) compounds of formula (I) which comprise alkoxysilane and amino groups

 wherein

R and R′ represent identical or different alkyl radicals comprising 1 to8 carbon atoms, preferably 1 to 4 carbon atoms, and

X, Y, Z represent identical or different alkyl or alkoxy radicalscomprising 1 to 4 carbon atoms, with the proviso that at least one ofthe radicals represents an alkoxy group,

characterised in that polyurethane prepolymers A) have an averagemolecular weight from 15,000 to 50,000 as calculated from their NCOcontent and NCO functionality.

The invention is based on the surprising observation that specialpolyurethane prepolymers which comprise alkoxysilane terminal groups andwhich have a very high molecular weight cure to give a tack-free productdespite their small number of crosslinking sites, and can be processedto form sealing materials which exhibit good elastomeric properties.

The isocyanate prepolymers A) which are used according to the inventionare produced in the manner known in the art from polyurethane chemistryby the reaction of a diisocyanate component i) with a polyol componentii) which is characterised in detail below.

Any prior art aliphatic, cycloaliphatic or aromatic diisocyanates withan isocyanate content of 20 to 60% by weight can be used according tothe invention as polyisocyanate component i). The terms “aromatic” and“cycloaliphatic” diisocyanates are to be understood to meandiisocyanates which contain at least one aromatic or cycloaliphatic ringper molecule, wherein, preferably, but not necessarily, at least one ofthe two isocyanate groups is directly linked to an aromatic orcycloaliphatic ring. Substances which are suitable and which arepreferred as component i) or as part of component i) are aromatic orcycloaliphatic diisocyanates of molecular weight range 174 to 300, suchas 4,4′-diphenylmethane diisocyanate, optionally in admixture with2,4′-diphenylmethane diisocyanate, 2,4-diisocyanatotoluene andindustrial mixtures thereof with preferably up to 35% by weight, withrespect to the mixture, of 2,6-diisocyanatotoluene,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI),bis-(4-isocyanatocyclohexyl)methane,1-isocyanato-1-methyl-4(3)-isocyanato-methyl-cyclohexane, and1,3-diisocyanato-6-methyl-cyclohexane, optionally in admixture with1,3-diisocyanato-2-methlylcyclohexane. Mixtures of the afore-mentionedisocyanates can also of course be used.

1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI) and/or2,4-diisocyanatotoluene and industrial mixtures thereof with preferablyup to 35% by weight, with respect to the mixture, of2,6-diisocyanatotoluene, are preferably used as component i).

For the production of polyurethane prepolymer A), diisocyanate componenti) is reacted with a polyol component ii). Polyol component ii)contains, as its main component, a polyoxyalkylene diol which has amolecular weight from 3000 to 20,000 (corresponding to an OH number from37.3 to 5.6), preferably 4000 to 15,000 (corresponding to an OH numberfrom 28 to 7.5). The polyoxyalkylene diols which are preferably usedaccording to the invention are those of the type known in the art frompolyurethane chemistry such as those which can be produced by theethoxylation and/or propoxylation of suitable starter molecules.Examples of suitable starter molecules include diols such as ethyleneglycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6hexanediol, 2-ethylhexanediol-1,3, and also include primary monoaminessuch as aliphatic amines, e.g. ethylamine or butylamine. Thepolyoxyalkylene diols which are preferably used have an averagemolecular weight, as calculated from their OH content and functionality,from 3000 to 20,000, preferably 4000 to 15,000, and have a maximumethylene oxide content of 20% by weight with respect to the total weightof the polyoxyalkylene diol.

The substances which are quite particularly preferred as component ii)are polypropylene oxide polyethers with a maximum total degree ofunsaturation of 0.04 milliequivalents/g and an average molecular weight,as calculated from their OH content and functionality, of 8000 to12,000.

The polyether polyols with a low degree of unsaturation which are mostpreferably used according to the invention are known in principle andare described, for example, in EP-A 283 148, U.S. Pat. Nos. 3,278,457,3,427,256, 3,829,505, 4,472,560, 3,278,458, 3,427,334, 3,941,849,4,721,818. 3,278,459, 3,427,335 and 4,355,188.

The polyether polyols which can be used according to the invention havea low degree of unsaturation and are preferably produced using metalcyanides as catalysts. The fact that the polyether polyols with a lowdegree of unsaturation which are most preferably used can be employedparticularly advantageously for the production of flexible, low-modulussealing materials must be said to be extremely surprising, sinceaccording to the prior art polyurethanes which are more ripid and whichhave a higher modulus are produced by the use of polyols of this type.

During the production of NCO prepolymers A), subsidiary amounts of lowmolecular weight dihydric and trihydric alcohols of molecular weight 32to 500 can optionally be used in conjunction. Suitable examples includeethylene glycol, 1,3-butandiol, 1,4-butandiol, 1,6-hexandiol, glycerineor trimeethylolpropane. The use in conjunction of low molecular weightalcohols is by no means preferred, however.

Moreover, during the production of NCO prepolymers A) subsidiary amountsof prior art polyfunctional polyether polyols can also be used inconjunction, although this is also by no means preferred.

Production of the polyurethane prepolymers which can be used accordingto the invention as component A) is effected by the reaction ofdiisocyanate component i) with diol component ii) within the temperaturerange from 40 to 120° C., preferably 50 to 100° C. whilst maintaining anNCO/OH equivalent ratio from 1.2:1 to 1.8:1, preferably from 1.3:1 to1.6:1. During the production of these polyurethane prepolymers, theamine or organometallic catalysts which are known in the art frompolyurethane chemistry can optionally be used in conjunction.

The polyurethane prepolymers A) which can be used according to theinvention have an NCO content from 0.21 to 0.56%. preferably from 0.28to 0.42%, corresponding to an average molecular weight from 15,000 to50,000, preferably from 20,000 to 40,000.

In the second stage of the method according to the invention, thepolyurethane prepolymers A) which can be used according to the inventionare reacted with compounds of formula (I)

wherein

R and R′ represent identical or different alkyl radicals comprising 1 to8 carbon atoms, preferably 1 to 4 carbon atoms, most preferably 1 to 2carbon atoms. and

X, Y, Z represent identical or different alkyl or alkoxy radicalscomprising 1 to 4 carbon atoms, with the proviso that at least one ofthe radicals represents, and preferably all 3 radicals represent, aC₁-C₈ alkoxy group.

Production of the compounds comprising alkoxysilane and amino groupswhich can be used according to the invention is effected as describedEP-A 596 360, by the reaction of aminoalkyl alkoxysilanes of formula(II)

wherein

X, Y and Z have the meanings given for formula (I),

with esters of maleic and/or fumaric acids, of formula (III)

ROOC—CH═CH—COOR′  (III),

 wherein

R and R, independently of each other, represent a C₁-C₈ alkyl.

Examples of suitable aminoalkyl alkoxysilanes of formula (II) include3-aminopropyl-trimethoxysilane, 3-aminopropyltriethoxysilane and3-aminopropyl-methyl-diethoxysilane; 3-aminopropyltrimethoxysilane and3-aminopropyltriethoxysilane are particularly preferred.

In the method according to the invention, the reaction of the NCOprepolymers with compounds of formula (I) which comprise alkoxysilaneand amino groups is conducted within a temperature range from 0 to 150°C., preferably 20-80° C., wherein the quantitative ratios are generallyselected so that 0.95 to 1.1 moles of aminosilyl compound are used permole of NCO groups used, 1 mole of aminosilyl compound is preferablyused per mole of NCO groups used. When higher reaction temperatures areemployed, a cyclocondensation reaction can occur in accordance with theteaching of EP-A 807 649. However, this is by no means troublesome andfrom time to time can even be advantageous.

The present invention further relates to the use of the polyurethaneprepolymers comprising alkoxysilane terminal groups according to theinvention as binders for the production of isocyanate-free, low-moduluspolyurethane sealing materials, preferably for the building sector.These sealing materials crosslink under the action of atmosphericmoisture, via a silane condensation polymerisation reaction.

For the production of sealing materials such as these, the polyurethaneprepolymers comprising alkoxysilane terminal groups according to theinvention can also be formulated together with customary plasticisers,fillers, pigments, drying agents, additives, light stabilisers,antioxidants. thixotropic agents, catalysts or bonding agents, andoptionally with other adjuvant substances and additives, according toknown methods for the production of sealing materials.

Examples of suitable fillers include carbon black, precipitated hydratedsilicas, mineral chalk materials and precipitated chalk materials.Examples of suitable plasticisers include phthalic acid esters, adipicacid esters, alkylsulphonic acid esters of phenol, or phosphoric acidesters.

Examples of thixotropic agents include pyrogenic hydrated silicas,polyamides, products derived from hydrogenated castor oil, and alsopolyvinyl chloride.

Organotin compounds and amine catalysts can be cited as suitablecatalysts for the curing reaction.

Examples of organotin compounds include: dibutyltin diacetate,dibutyltin dilaurate, dibutyltin bis-acetoacetonate and tincarboxylates, such as tin octoate for example. The aforementioned tincatalysts can optionally be used in combination with amine catalystssuch as aminosilanes or diazabicyclooctane.

Drying agents which are particularly suitable include alkoxysilylcompounds such as vinyl trimethoxysilane, methyl trimethoxysilane,i-butyl trimethoxysilane and hexadecyl trimethoxysilane.

The known functional silanes are used as such as bonding agents, such asaminosilanes of the aforementioned type, for example, and alsoaminoethyl-3-aminopropyl-trimethoxt- and/orN-aminoethyl-3-aminopropyl-methyl-dimethoxysilane. epoxysilanes and/ormercaptosilanes.

The crosslinked polymers are distinguished by their outstandingextensibility and at the same time by their low modulus. In particular,products based on the polyoxypropylene glycols with a low total degreeof unsaturation which are preferably used as diol component ii) aredistinguished by their low modulus, excellent mechanical properties andby their low degree of surface tack.

EXAMPLES Example 1

4000 g of a polypropylene glycol with an OH number of 14 and with adegree of unsaturation of 0.005 milliequivalent/g (Acclaim 8200;manufactured by Arco) were pre-polymerised with 166.5 g isophoronediisocyanate at 100° C. until the theoretical NCO content of 0.5% wasreached. The polyurethane prepolymer obtained had a calculated averagemolecular weight of 16,600. After cooling the batch to 60° C., 175.5 gN-(3-trimethoxysilylpropyl)aspartic acid diethyl ester (preparedaccording to EP-A 596 360, Example 5) were rapidly added drop-wisethereto, and the mixture was stirred until isocyanate bands were nolonger observed in the IR spectrum. The polyurethane prepolymercomprising alkoxysilyl terminal groups which was obtained had aviscosity of 26,000 mPas (23° C.).

A film which was cast on to a glass plate cured overnight, usingdibutyltin diacetate as a catalyst, to form a clear, highly flexibleplastic with a Shore A hardness of 13.

Example 2

2000 g of a polyether diol with an OH number of 28, which was producedby the propoxylation of propylene glycol and subsequent ethoxylation ofthe propoxylation product (PO/EO ratio 80:20), were pre-polymerised with104.4 g toluene 2,4-diisocyanate at 80° C. until the theoretical NCOcontent of 0.6% was reached. The polyurethane prepolymer obtained had acalculated average molecular weight of 21,000. Alter cooling the batchto 60° C. 64.6 g N-(3-trimethoxysilyl-propyl)aspartic acid dimethylester (prepared according to EP-A 596 360, Example 4) were rapidly addeddrop-wise thereto until isocyanate bands were no longer observed in theIR spectrum. The polyurethane prepolymer comprising alkoxysilyl terminalgroups which was obtained had a viscosity of 96,000 mPas (23° C.).

A film which was cast on to a glass plate cured overnight, usingdibutyltin diacetate as a catalyst, to form a clear, highly flexibleplastic with a Shore A hardness of 9.

Example 3

4000 g of a polypropylene glycol with an OH number of 14 and with adegree of unsaturation of 0.005 milliequivalent/g (Acclaim 8200,manufactured by Arco) were pre-polymerised with 155.4 g isophoronediisocyanate at 100° C. until the theoretical NCO content of 0.4% wasreached. The polyurethane prepolymer obtained had a calculated averagemolecular weight of 21,000. After cooling the batch to 60° C. 140.4 gN-(3-trimethioxysilylpropyl)aspartic acid diethyl ester (preparedaccording to EP-A 596 360, Example 5) were rapidly added drop-wisethereto, and the mixture was stirred until isocyanate bands were nolonger observed in the IR spectrum. The polyurethane prepolymercomprising alkoxysilyl terminal groups which was obtained had aviscosity of 28,000 mPas (23° C.).

A film which was cast on to a glass plate cured overnight, usingdibutyltin diacetate as a catalyst, to form a flexible plastic with aShore A hardness of 15.

Example 4

5300 g of a polypropylene glycol with an OH number of 10.6 and with adegree of unsaturation of 0.005 milliequivalent/g (Acclaim 12200,manufactured by Arco) were pre-polymerised with 147.9 g of a commercialmixture containing 80% by weight toluene 2,4-diisocyanate and 20% byweight toluene 2,6-diisocyanate at 80° C. until the theoretical NCOcontent of 0.54% was reached. The polyurethane prepolymer obtained had acalculated average molecular weight of 15,500. After cooling the batchto 60° C., 226.1 g N-(3-trimethoxysilylpropyl)aspartic acid dimethylester (prepared according to EP-A 596 360, Example 4) were rapidly addeddrop-wise thereto, and the mixture was stirred until isocyanate bandswere no longer observed in the IR spectrum. The polyurethane prepolymercomprising alkoxysilyl terminal groups which was obtained had aviscosity of 25,000 mPas (23° C.).

A film which was cast on to a glass plate cured overnight, usingdibutyltin diacetate as a catalyst, to form a flexible plastic with aShore A hardness of 12.

Example 5

5300 g of a polypropylene glycol with an OH number of 10.6 and with adegree of unsaturation of 0.005 milliequivalent/g (Acclaim 12200;manufactured by Arco) were pre-polymerised with 166.5 g of isophoronediisocyanate at 100° C. until the theoretical NCO content of 0.38% wasreached. The polyurethane prepolymer obtained had a calculated averagemolecular weight of 22,000. After cooling the batch to 60° C., 175.5 gN-(3-trimethoxysilylpropyl)aspartic acid diethyl ester (preparedaccording to EP-A 596 360, Example 5) were rapidly added drop-wisethereto, and the mixture was stirred until isocyanate bands were nolonger observed in the IR spectrum. The polyurethane prepolymercomprising alkoxysilyl terminal groups which was obtained had aviscosity of 30,000 mpas (23° C.).

A film which was cast on to a glass plate cured overnight, usingdibutyltin diacetate as a catalyst, to form a flexible plastic with aShore A hardness of 12.

Example 6

Production of an Isocyanate-free Polyurethane Sealing Material

The following components were processed in a commercially availableplanetary mixer to produce a ready-to-use sealing material:

41.6 parts by weight of the prepolymer from Example 3 14.6 parts byweight diiso-undecyl phthalate (plasticiser) 0.20 parts by weightdibutyltin bis-acetoacetonate (10% solution in solvent naphtha 100) 1.50parts by weight vinyl trimethoxysilane 41.6 parts by weight precipitatedchalk (Type: Socal U1S2).

The mixture was dispersed for 10 minutes at a pressure of 100 mbar,whereupon the internal temperature rose to 60° C.

0.5 parts by weight N-aminoethyl-3-aminopropyl-methyldimethoxysilanewere subsequently added and were incorporated by stirring for 10 minutesat a pressure of 100 mbar.

The sealing material which was thus produced exhibited excellentstability, adhered to almost all substrates, and cured with a skinformation time of about 1.5 hours.

What is claimed is:
 1. A polyurethane prepolymer having alkoxysilaneterminal groups which are produced by the reaction of A) a linearpolyurethane prepolymer with a number-average molecular weight from15,000 to 50,000, as calculated from its NCO content and NCOfunctionality, produced by the reaction of i) an aromatic, aliphatic orcycloaliphatic diisocyanate component having an NCO content of 20% to60% by weight, with ii) a polyol component which comprises apolypropylene oxide polyether diol having a maximum total degree ofunsaturation of 0.04 milliequivalents/g and a number average molecularweight from 8000 to 20,000, as calculated from its OH content andfunctionality, with B) a compound of formula (I)

 wherein R and R′ represent identical or different alkyl radicalscomprising 1 to 8 carbon atoms, and X, Y, Z represent identical ordifferent alkyl or alkoxy radicals comprising 1 to 4 carbon atoms, withthe proviso that at least one of the radicals represents an alkoxygroup.
 2. The polyurethane prepolymer of claim 1, wherein thepolyurethane prepolymer A) has a number average molecular weight from20,000 to 40,000.
 3. The polyurethane prepolymer of claim 1, wherein X,Y and Z, independently of each other, represent methoxy or ethoxy.
 4. Asealing material comprising the polyurethane prepolymer of claim
 1. 5.The polyurethane prepolymer of claim 1 wherein R and R′ representidentical or different alkyl radicals having 1 to 4 carbon atoms.
 6. Thepolyurethane prepolymer of claim 2 wherein R and R′ represent identicalor different alkyl radicals having 1 to 4 carbon atoms.
 7. Thepolyurethane prepolymer of claim 3 wherein R and R′ represent